Vacuum breakdown in a multibeam configuration of a magnetic dipole wave

We study the breakdown of vacuum in multipetawatt laser fields of a multibeam configuration corresponding to a converging magnetic dipole wave. Using three-dimensional numerical simulation by the particle-in-cell method, the threshold total laser radiation power required for vacuum breakdown is determined as a function of the number of laser beams. It is shown that a minimum threshold breakdown power of 14 PW is reached when use is made of 12 beams; with a decrease in the number of beams to two to six, the threshold power increases and is set at the level of 18 PW. The dependence of the development rate of a quantum-electrodynamic cascade on the number of laser beams in a wide power range is determined. It is shown that fluctuations in the power of each of the beams have little effect on both the breakdown threshold and the rate of cascade development.